Context : Clouds form in atmospheres of brown dwarfs and planets .
The cloud particle formation processes , seed formation and growth/evaporation , are very similar to the dust formation process studied in circumstellar shells of AGB stars and in Supernovae .
Cloud formation modelling in substellar objects requires gravitational settling and element replenishment in addition to element depletion .
All processes depend on the local conditions , and a simultaneous treatment is required .

Aims : We apply new material data in order to assess our cloud formation model results regarding the treatment of the formation of condensation seeds .
We re-address the question of the primary nucleation species in view of new ( TiO _ { 2 } ) _ { N } -cluster data and new SiO vapour pressure data .

Methods : We apply the density functional theory ( B3LYP , 6-311G ( d ) ) using the computational chemistry package Gaussian 09 to derive updated thermodynamical data for ( TiO _ { 2 } ) _ { N } -clusters as input for our TiO _ { 2 } seed formation model .
We test different nucleation treatments and their effect on the overall cloud structure by solving a system of dust moment equations and element conservation for a pre-scribed Drift-Phoenix atmosphere structure .

Results : Updated Gibbs free energies for the ( TiO _ { 2 } ) _ { N } -clusters are presented , and a slightly temperature dependent surface tension for T=500 \ldots 2000K with an average value of \sigma _ { \infty } = 480.6 erg cm ^ { -2 } .
The TiO _ { 2 } -seed formation rate changes only slightly with the updated cluster data .
A considerably larger effect on the rate of seed formation , and hence on grain size and dust number density , results from a switch to SiO-nucleation .
The question about the most efficient nucleation species can only be answered if all dust/cloud formation processes and their feedback are taken into account .
Despite the higher abundance of SiO over TiO _ { 2 } in the gas phase , TiO _ { 2 } remains considerably more efficient in forming condensation seeds by homogeneous nucleation .
The paper discussed the effect on the cloud structure in more detail .

Conclusions :